1. Field of the Invention
The present invention relates to hydrophones. More particularly, it relates to fiber optic hydrophone assemblies which can be easily taken apart and repaired, rather than being discarded when a defect arises.
2. Description of the Related Art
Hydrophones are well known in the art of acoustic sensing devices. Hydrophones are typically used in underwater operations, and are often configured into cylindrical shapes. During the assembly of conventional fiber optic hydrophones, optical fibers and other components are inserted into an inner chamber without the benefit of visual inspection. This process presents a risk of breakage and subsequent discarding of expensive assembly components. This process also makes diagnosis of sensor malfunctions difficult, since key components are often hidden from view. While components such as splices and couplers are typically tacked to the inside walls or other structures within this chamber, optical fibers must remain unrestrained to complete the insertion process. This causes the fibers to vibrate freely, and to impart a small acceleration sensitivity to the hydrophone device, which is only intended to be sensitive to acoustic pressure. This is particularly undesirable in applications where other sensors are used to sense the motion in the acoustic medium, and “crosstalk” among the sensors can reduce the fidelity of the sensing system.
Furthermore, cylindrically configured hydrophones also require optical fibers to pass into a cavity which is then sealed, to protect it from ambient pressure. These points of fiber penetration require small segments of the fiber to be embedded in stiff epoxies at points of high stress build-up, and are prone to breaking the fiber.
The present invention provides a solution to these problems. This invention provides a re-enterable, end-to-end hydrophone assembly which is at least partially transparent, so that the routing of the hydrophone fibers is visible during all phases of assembly and operation. This provides an advantage in that the hydrophone assembly can be easily disassembled, repaired, and reassembled.
The inventive assembly may be used in various applications, such as in producing hydrophones for use in towed arrays or bottom-mounted cables for undersea surveillance or surveys. This invention may be particularly useful in seismic applications, where large numbers of sensors are required, and where the cost and skill level of assembly operators is very high.
Several conventionally acoustic sensing assemblies are known. U.S. Pat. No. 5,363,342 teaches the use of concentric mandrels for fiber optic acoustic sensing. In particular, it describes two fiber-wrapped mandrels with a support mandrel between them. U.S. Pat. No. 5,285,424 also relates to concentric mandrels. It teaches a two-mandrel sensor without a support mandrel. Specifically, it teaches the use of two hollow concentric mandrels with a means for spacing them apart with a watertight, sealed cavity between them and a reference coil in the cavity. U.S. Pat. No. 6,288,975 teaches an end-to-end mandrel having a reduced diameter, a grooved flexible interlink, and hemispherically shaped end caps.
The present invention offers advantages over such known assemblies. For example, the related art offers only non-visible, closed assemblies, wherein hydrophone components are stuffed into mandrels thus risking breakage. This problem is solved by the present invention which offers an at least partially transparent reference housing which enables a user to view the inside of the assembly. The hydrophone assembly of the invention can be easily fabricated due to the full visibility of the fiber during fabrication. This also allows one to better control the component position and routing. Furthermore, the fabrication of the hydrophone assembly of the present invention can be made reversible. That is, the hydrophone assembly can be taken apart, repaired, and reassembled without having to scrap the expensive hydrophone components such as optical fibers and the like.